feat: add antigravity workflows playbooks and orchestration skill

Introduce the first Antigravity Workflows foundation with machine-readable workflow metadata, a dedicated orchestration skill, and onboarding docs that explain when to use bundles versus workflows. This reduces multi-skill friction for common goals like SaaS MVP delivery, security audits, AI agent builds, and browser QA.

Co-authored-by: Cursor <cursoragent@cursor.com>

skills/antigravity-workflows/SKILL.md

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+---
+name: antigravity-workflows
+description: "Orchestrate multiple Antigravity skills through guided workflows for SaaS MVP delivery, security audits, AI agent builds, and browser QA."
+source: self
+risk: none
+---
+
+# Antigravity Workflows
+
+Use this skill to turn a complex objective into a guided sequence of skill invocations.
+
+## When to Use This Skill
+
+Use this skill when:
+- The user wants to combine several skills without manually selecting each one.
+- The goal is multi-phase (for example: plan, build, test, ship).
+- The user asks for best-practice execution for common scenarios like:
+  - Shipping a SaaS MVP
+  - Running a web security audit
+  - Building an AI agent system
+  - Implementing browser automation and E2E QA
+
+## Workflow Source of Truth
+
+Read workflows in this order:
+1. `docs/WORKFLOWS.md` for human-readable playbooks.
+2. `data/workflows.json` for machine-readable workflow metadata.
+
+## How to Run This Skill
+
+1. Identify the user's concrete outcome.
+2. Propose the 1-2 best matching workflows.
+3. Ask the user to choose one.
+4. Execute step-by-step:
+   - Announce current step and expected artifact.
+   - Invoke recommended skills for that step.
+   - Verify completion criteria before moving to next step.
+5. At the end, provide:
+   - Completed artifacts
+   - Validation evidence
+   - Remaining risks and next actions
+
+## Default Workflow Routing
+
+- Product delivery request -> `ship-saas-mvp`
+- Security review request -> `security-audit-web-app`
+- Agent/LLM product request -> `build-ai-agent-system`
+- E2E/browser testing request -> `qa-browser-automation`
+
+## Copy-Paste Prompts
+
+```text
+Use @antigravity-workflows to run the "Ship a SaaS MVP" workflow for my project idea.
+```
+
+```text
+Use @antigravity-workflows and execute a full "Security Audit for a Web App" workflow.
+```
+
+```text
+Use @antigravity-workflows to guide me through "Build an AI Agent System" with checkpoints.
+```
+
+```text
+Use @antigravity-workflows to execute the "QA and Browser Automation" workflow and stabilize flaky tests.
+```
+
+## Limitations
+
+- This skill orchestrates; it does not replace specialized skills.
+- It depends on the local availability of referenced skills.
+- It does not guarantee success without environment access, credentials, or required infrastructure.
+- For stack-specific browser automation in Go, `go-playwright` may require the corresponding skill to be present in your local skills repository.
+
+## Related Skills
+
+- `concise-planning`
+- `brainstorming`
+- `workflow-automation`
+- `verification-before-completion`

skills/antigravity-workflows/resources/implementation-playbook.md

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+# Antigravity Workflows Implementation Playbook
+
+This document explains how an agent should execute workflow-based orchestration.
+
+## Execution Contract
+
+For every workflow:
+
+1. Confirm objective and scope.
+2. Select the best-matching workflow.
+3. Execute workflow steps in order.
+4. Produce one concrete artifact per step.
+5. Validate before continuing.
+
+## Step Artifact Examples
+
+- Plan step -> scope document or milestone checklist.
+- Build step -> code changes and implementation notes.
+- Test step -> test results and failure triage.
+- Release step -> rollout checklist and risk log.
+
+## Safety Guardrails
+
+- Never run destructive actions without explicit user approval.
+- If a required skill is missing, state the gap and fallback to closest available skill.
+- When security testing is involved, ensure authorization is explicit.
+
+## Suggested Completion Format
+
+At workflow completion, return:
+
+1. Completed steps
+2. Artifacts produced
+3. Validation evidence
+4. Open risks
+5. Suggested next action